The fluid pH inside a flowline or pipeline is an important parameter for determining the corrosion mechanism in the flowline or pipeline and applying mitigation methods. Fluid pH further influences the partitioning of oilfield chemicals, so that a good understanding of fluid pH is important for oilfield chemical management. One common industry approach to determine pH is to conduct water chemistry analysis on the depressurized water sample and then back calculate the original pH based on the levels of bicarbonate, acetic acid/acetate, carbon dioxide (CO2) and hydrogen sulfide (H2S). However, the accuracy of this type of calculation is often limited by the accuracy of water chemistry analysis, especially the ratio between acetic acid and acetate. Currently there is no analytical technique able to distinguish acetic acid from acetate during the water chemistry analysis. Furthermore, certain species in the water sample, such as acetic acid and bicarbonate, are subject to change during the sampling and shipping process even before the analysis. Because of all those uncertainties, the pH prediction for a production unit can vary significantly between samples, hindering the determination of the corrosion mechanism in the sample, as well as potential corrosion mitigation methods. What is needed is a method for accurately measuring pH in a flowline or pipeline.
The formation of biofilms is another factor in flowline or pipeline corrosion. Biofilms are accumulations of microorganisms along with organic and inorganic deposits on surfaces. Biofilms form through the attachment and growth of planktonic (free-floating) microorganisms that are present in all aqueous environments, including water extracted from a hydrocarbon well. It has been discovered that certain biofilms that form on the interior surfaces of flowlines, pipelines, and pressure vessels can, when left uncontrolled, cause significant corrosion to the metal substrate. Such corrosion is referred to as microbiologically influenced corrosion (MIC). It is hence important to be able to collect, quantify and characterize such oilfield biofilms as part of a robust facility integrity program. Collection and analysis of biofilms helps determining the type and degree of MIC expected within a particular production environment. The most common point of access to biofilm for diagnosis and monitoring of MIC are corrosion coupons. However, many facilities lack corrosion coupons or cannot install corrosion coupons at locations of water drop out, which is where formation of corrosive biofilm is possible. What is needed is a method of testing corrosion coupons in an environment that maximizes their effectiveness.